Reactions in the matrix and interface of the Fe–SiC metal matrix composite system

Fe–SiC metal matrix composite (MMC) was produced by the use of hot isostatic pressing (HIP) or sintering for consolidation. The SiC in the MMC was in the forms of particulates and chopped fibers. The effect of exposure of the MMC to high temperatures for long time, up to 1.4×104 s, was obtained by heat treatment of the HIPed or sintered specimens. A small reaction zone of ∼0.5–1 μm, composed of iron silicides, was observed in specimens HIPed at 1173 K at a pressure of 150 MPa. Cursory mechanical tests indicate an increase in the ultimate tensile strength and the yield strength of 33.1 and 12.6% of the as HIPed specimens, respectively, when the SiC content was 3% by volume. C, originating from the SiC and dissolved in Fe, induces changes in the matrix when the MMC is exposed to high temperatures, leading to the formation of the familiar transformation products. Strengthening by modification of the Fe matrix under controlled conditions is a unique feature of the Fe–SiC MMC system. The kinetics of the reaction zone formation was investigated and it was found that its growth is diffusion controlled and occurs with an activation energy of 205.4 kJ mol−1. The reaction zone might act as a diffusion barrier preventing fiber degradation as long as the conditions of thermal effects are reasonable, but exposure of the MMC to high temperatures for extended time can result in severe fiber damage. A mechanism is suggested for the reaction zone formation.